Profiled extrudate of polymeric materials are widely used in automobile body applications such as molding pieces. For instance, body side moldings or wheel well moldings are frequently used to protect a vehicle body from impact damage and to protect edges of sheet metal panels from corrosion. Most of these molding pieces are extruded of thermoplastic materials such as PVC (polyvinyl chloride), thermoplastic rubber, thermoplastic urethane, or other flexible polymeric materials. PVC is one of the most widely used materials for its low cost and good physical properties.
Molding pieces such as body side moldings may be extruded of a plastic material alone or extruded of a plastic material on a metal reinforcing substrate by an extrusion coating process. In an extrusion coating process where plastic materials are combined with a more rigid substrate, a cross-head extrusion technique is used in which a continuous length of metal reinforcing substrate is pulled through an extrusion die at 90.degree. angle to the direction of the plastic flow while molten plastic material is being extruded onto the metal substrate. The metal reinforcing substrate is usually cleaned and dried through a multi-station process and formed by a series of metal roll formers prior to the entry into the extrusion die.
In the manufacturing of automobile body side moldings, the aesthetic appearance of the molding is one of the most important criteria that must be satisfied. In the extrusion of vinyl or vinyl/metal substrate reinforced molding pieces, the quality of the surface appearance of the molding pieces obtained is dependent upon many variables. For instance, these variables include the material composition, the extrusion temperature, the extrusion pressure, the extrusion rate, the cooling rate, etc. When a high gloss surface appearance is desired on a PVC molding piece, two common approaches are traditionally used.
First, a high gloss film may be permanently laminated to the outer periphery of a molding piece. This approach, even though producing an aesthetically pleasing appearance, has the drawback of cost penalty due to the high cost incurred in using high gloss films. Moreover, laminated molding pieces have potential de-lamination problems, especially when the molding pieces are subjected to severe environmental exposures.
The second approach of achieving a high gloss surface appearance on a PVC molding is by removably laminating a smooth film to the surface of the molding piece immediately after extrusion and then stripping off the film after the molding piece is cooled to room temperature. This process is described in detail in U.S. Pat. No. 4,849,045 assigned to the same assignee as the present invention. In this method, even though a smooth high gloss surface can be obtained, some additional processing parameters must be carefully observed. Moreover, only a single gloss level may be achieved by the use of a particular film having a fixed surface finish. To obtain a different gloss appearance, a different type of film must be used.
It is, therefore, an object of the present invention to provide a method of producing extrudates of polymeric materials having a desirable surface gloss finish.
It is another object of the present invention to provide a method of producing extrudates of polymeric materials having either an enhanced or reduced surface gloss finish.
It is a further object of the present invention to provide a method of producing extrudates of polymeric materials having either an enhanced or reduced surface gloss finish by simply varying some processing conditions.
It is yet another object of the present invention to provide a method of producing extrudates of polymeric materials having either an enhanced or reduced surface gloss finish without requiring a lamination process.